I. Technical Field.
The present invention relates to a barrier-film forming apparatus, a barrier-film forming method, and a barrier-film coated container for uniformly forming a barrier film that provides a gas barrier property to a resin container, for example.
II. Description of the Related Art
Recently, an approach has been adopted to coat an inner face of a polyethylene terephthalate (PET) bottle, which is one type of plastic containers, with a film having a high barrier property, for example a carbon film such as diamond-like carbon (DLC) or a silica film, to prevent transmission of external oxygen or transmission of internal carbon dioxide (for example, from carbonated beverage). Various film depositing apparatuses for that purpose are proposed (Japanese Patent Application Laid-open No. H8-53116, Japanese Patent No. 2788412 (Japanese Patent Application Laid-open No. H8-53117), WO2003/101847, Japanese Patent No. 3643813(Japanese Patent Application Laid-open No. 2003-237754), Japanese Patent Application Laid-open No. 2005-247431 and Japanese Patent Application Laid-open No. 2000-230064). Applications of this approach are used for medical containers, food containers, and fuel tanks to prevent transmission of oxygen, hydrogen, and fuel, or transmission or absorption of aroma, and the like.
As a film forming apparatus that forms a carbon film on a plastic container using high-frequency plasma chemical vapor deposition (CVD), an apparatus according to Japanese Patent No. 3643813 (Japanese Patent Application Laid-open No. 2003-237754), which is a basic invention that achieves coating of inside of a container, will be explained with reference to FIG. 38.
As shown in FIG. 38, a barrier-film forming apparatus forms a film on an inner face of a plastic container 12 having a mouth 11 by discharge plasma. This barrier-film forming apparatus includes an external electrode 13 including an upper external electrode 13-1 and an lower external electrode 13-2 and having a size to enclose an outer circumference of the plastic container 12, and a spacer 25 including a dielectric that is interposed at least between the mouth and a shoulder of the container and the external electrode 13 when the plastic container 12 is inserted therein. The barrier-film forming apparatus further includes an exhaust pipe 14 attached to an end face of the external electrode 13 on the side where the mouth 11 is located, with an insulating member 26 interposed therebetween, and an internal electrode 17 that is inserted into the plastic container from the side of the exhaust pipe 14 into the plastic container 12 within the external electrode 13 to be connected to a ground side and has a gas flow channel 16 drilled to blow out medium gas 19. The barrier-film forming apparatus further includes an exhaust unit (not shown) attached to the exhaust pipe 14, a gas supplier (not shown) that supplies the medium gas 19 to the internal electrode 17, and a high-frequency power source 18 connected to the external electrode 13. Reference numeral 20 denotes a gas blowout hole made of an insulating member mounted at a tip of the gas flow channel 16.
The external electrode 13 is installed in a cylindrical earth shield 22 having flanges 21a and 21b at upper and lower ends, respectively. The cylindrical earth shield 22 is mounted on an annular base 23. A disk insulating plate 24 is placed between the annular base 23 and the bottom of the external lower electrode 13-2. The cylindrical insulating member 26 is provided at the tip of the gas flow channel 16 of the internal electrode 17 to prevent local concentration of plasma.
The spacer 25 is fixed by a screw (not shown) threaded therein from the annular insulating member 26 placed on the spacer 25. By inserting and fixing the spacer 25 to an upper part of the external electrode 13 in this way, the mouth and the shoulder of the plastic container 12 are positioned in a cavity of the disk spacer 25, and the outer circumference of the plastic container 12 except for the mouth and the shoulder is positioned at the inner face of the external electrode 13, when the plastic container 12 is inserted from the bottom of the external electrode 13. The gas exhaust pipe 14 having upper and lower flanges 31a and 31b is placed on the upper flange 21a of the earth shield 22 and an upper surface of the annular insulating member 26. A cover 32 is attached to the upper flange 31a of the exhaust pipe 14.
A method of coating the plastic container with a carbon film using the apparatus with the configuration as described above will be explained.
The plastic container 12 is first inserted into the external electrode 13, and internal gas is evacuated through the exhaust pipe 14. When a prescribed vacuum is obtained (typical value: 10−1 to 10−5 Torr), medium gas G is supplied to the internal electrode 17 at a flow rate of 10 to 200 mL/min, for example, and blown out into the plastic container 12 through the gas blowout hole 20 of the internal electrode 17, while the evacuation is continued. As the medium gas, an aliphatic hydrocarbon, an aromatic hydrocarbon, an oxygenated hydrocarbon, or a nitrogenous hydrocarbon, such as benzene, toluene, xylene, and cyclohexane is used. A pressure in the plastic container 12 is set at 2×10−1 to 1×10−2 Torr, for example, depending on balance between an amount of the gas supplied and an amount of air evacuated. The high-frequency power source 18 then applies high-frequency power of 50 to 2000 watts to the external electrode 13 through a matching box 36 and a radio-frequency (RF) input terminal 35.
The application of the high-frequency power to the external electrode 13 generates plasma between the external electrode 13 and the internal electrode 17. At this time, the plastic container 12 is housed within the external electrode 13 with almost no space therebetween, and thus the plasma is generated in the plastic container 12. The medium gas G is dissociated or further ionized by the plasma, and then a film-forming seed for forming a carbon film is generated. This film-forming seed is deposited on the inner face of the plastic container 12, thereby forming a carbon film. When a predetermined thickness of the carbon film is formed, the application of the high-frequency power is stopped, the supply of the medium gas is stopped, the remaining gas is evacuated, and nitrogen, noble gas, or air is supplied within the external electrode 13 to bring the space back to the atmospheric pressure. The plastic container 12 is then removed from the external electrode 13. This method takes two to three seconds to form a carbon film of a thickness of 20 to 30 nanometers.